Inclined air core solenoid fields for lasers

ABSTRACT

A laser plasma discharge bore or tube having one or more pairs of air core solenoids in parallel or angularly disposed flux aligned positions across the discharge bore to provide linear discharge magnetic fields proportional to current for stabilized laser action that is uniform and non-saturable and adjustable in amplitude and applicable to cross-field lasers and cross-field scan lasers alike.

limited States Patent 1 Wayne [11] 3,743,961 [45 July 3,1973

[54] INCLINED AIR coma SOLENOID FIELDS ron LASERS [75] Inventor: RobertJoseph Wayne, East Hartford, Conn.

[73] Assignee: The United States of America as 1 represented by theSecretary of the Navy, Washington, D.C.

{22] Filed: Feb. 9, 1972 [21] Appl. No.: 224,788

[52] US. Cl 331/945, 330/43, 350/151,

' 315/344, 313/79 [51] Int. Cl. H018 3/10 [58] Field of Search 331/945;350/151;

[56] References Cited UNITED STATES PATENTS 3,521,193 7/1970 Wingfield331/945 Primary Examiner-Ronald L. Wibert Assistant Examiner-R. J.Webster Att0meyR. S. Sciascia and P. S. Collignon [5 7] ABSTRACT A laserplasma discharge bore or tube having one or more pairs of air coresolenoids in parallel or angularly disposed flux aligned positionsacross the discharge bore to provide linear discharge magnetic fieldsproportional to current for stabilized laser action that is uniform andnon-saturable and adjustable in amplitude and applicable to cross-fieldlasers and cross-field scan lasers alike.

4 Claims, 10 Drawing Figures PAIENIEDJUL 3 I973 CURRFNT CONTRQL COILWIDTH COIL WIDTH MCOIL WIDTH ADJUSTABLE CONSTANT PAIEITE IIIII' ma 374398-1 SOLENOID PARTIALLY REFLECTING SURFACES FOLDED DISCHARGE SOLENOIDFig.6

NEW NET FIELD MAGNETIC FIELD CONTOUR MAGNETIC FIELD STRENGTH a PLASMIAPOSITION AT CAT'HODE Z (VARIABLE) II PLASMA POSITIONIIOI TIME VARYINGFIELD B0 STABLE CONTOURS(AT SOME TIMEm I I I I l I I T o CHANNEL WIDTH XPLASMA POSITION ATANODE (PINNED) Fig.7

f PAIENIEBM a ma SIEETSN3 FIELD FROM FERRITE MAGNETS ALONE NEW NET FIELD(+10 AMPS. THRU COILS) NEW NET FIELD (-lOAMPS THRU COILS) INCLINED AIRCORE SOLENOID FIELDS FOR LASERS BACKGROUND OF THE INVENTION Thisinvention relates to optical lasers and more particularly to the meansof producing magnetic lines of flux across the laser discharge bore in auniform, linear and inclined flux density profile that is adjustable andcontrollable in intensity to produce uniform lasing discharge.

Present means for generating magnetic fields are by using large heavyiron core electromagnets coupled to long pole pieces which are arrangedabove and below and to the sides of a laser discharge axis. To increasethe field strength there must be an increase in current through eachiron core electromagnetic since the gap is fixed. The usual suchelectromagnet poles are about twelve inches long and about one andone-fourth inches wide separated by one inch to provide the necessaryfield strength. The field increases non-linearly with current due tosaturation of the core and falls off steeply from the centerline of thepole pieces. The only way to change the field taper, or slope at thelaser discharge, is to physically move the entire pole piece assemblyalong the laser. Also, the range of slopes which are constant foronehalf inch or more (assuming this to be the diameter of the dischargebore) is limited as are the values of high magnitude flat sloped fieldswhich would require much broader pole pieces. Such high peaked andnarrow magnetic flux fields are mostly useless because of the wrongslope sign and the majority of the rest of the field is useless for thereason that there is too small a field in the fringe area and the fieldextending on either side of the discharge bore is not needed due tolaser discharge tube fins. Permanent magnets, such as light weightferrites, are without a doubt the most economical way of producing largefields over long lengths. Unfortunately, when used in conjunction withlong pole pieces and electomagnet coils the same problems are faced aswith iron core electromagnets except that the input power requirementsare reduced to achieve the needed field magnitudes while increasing theweight of the structure.

SUMMARY OF THE INVENTION The present invention conceives the use ofpairs of air core coils or solenoids to generate magnetic field profileslinearly with current across a laser discharge bore. Since there is noiron, the field increases linearly with current and is generally uniformacross the gap. Further, iron return flux paths are not necessary. Ifthe coils or solenoids are inclined with respect to each other, slopingfield profiles are produced and the slope is very nearly constant,positive, and linear with current. Such solenoid pairs can be usedparallel or inclined across either cross-field laseror cross-field scanlaser discharge bores and the optical path of any folded cavity can gothrough the coil, when necessary, without destroying the linear,adjustable, and taper characteristics of the air core field profiles.While the invention is readily useful for CO lasers, it is useful forall laser discharge. It is accordingly, a general object of thisinvention to provide a laser discharge with air core coils or solenoidspaired at relative angles to produce controlled linearmagnetic fieldprofiles of adjustable slope and intensity across a laser discharge boreof uniform flux density which will not saturate or distort.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and theattendant advantages, features and uses will become more apparent tothose skilled in the art of lasers as a more detailed descriptionproceeds when considered along with the accompanying drawings, in which:

FIG. 1 illustrates a parallel arrangement of solenoids with a lasingtube therebetween in accordance with the invention;

FIG. 2 illustrates solenoid coils in relative inclined or angularrelation with a lasing tube therebetween;

FIG. 3 illustrates a graph of the flux density with respect to coil sizeand current applied for parallel solenoids;

FIG. 4 illustrates in graph form the flux density with respect to coilsize and current applied for about 15 angular relation of the solenoidcoils;

FIG. 5 illustrates the fiux density with respect to current with angularrelation of the air core coils similar to FIG. 4 but a greater angle,such as 30;

FIG. 6 illustrates a folded discharge lasing tube with solenoid coilsadjustably affixed in angular relation;

FIG. 7 illustrates a plot of the magnetic field geometry for horizontalline scanners using specially inclined air core solenoids as illustratedin FIG. 6;

FIG. 8 illustrates the use of a permanent magnetic within solenoid coilswith a lasing tube therebetween;

FIG. 9 plots the adjustment range of a lasing fixture as shown in FIG.8; and

FIG. 10 illustrates stacked solenoid coils-with a lasing tubetherebetween.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly toFIG. 1 a lasing discharge tube 10 of a cross-field scan laser orcross-field laser device is shown passing between solenoid coils 11 and12 spaced in parallel relation to cause flux lines from the coil centersto pass through the lasing tube. Coils 11 and 12 should be of sufficientsize to establish the flux field completely across the diameter of thelasing tube 10. The flux density, or B in guass, is independent of coildiameter, area, or shape and accordingly the coils could have a lengthof 20:1 or any shape to ideally fit the geometry of the laser dischargebore. The coils 11 and 12 are coupled in series from the lead 14 withthe leads coupled in common and the lead 16 coupled to a fixed potentialor one pole of the voltage supply system. The lead 14 is preferably inthe circuit of a current control device 17 such as a rheostat,potentiometer, variable resistance, or other suitable device to controlcurrent out of a voltage source 18 through the coils to the fixed orground potential, as well understood by those skilled in the art. Inthis manner the current through the solenoid coils 11 and 12 isadjustable by the current control 17 to increase or decrease the fluxdensity generated by the coils. FIG. 3 illustrates the flux density, B,in gauss relative to several ampere increments to produce the fiuxdensity profile as shown in relation to the coil width. It is to beunderstood that in practicing the invention paired solenoids may be usedorthogonally to produce crossed horizontal and vertical fields, ifdesired.

Referring more particularly to FIG. 2 the lasing tube 10 is illustratedas passing between coils 21 and 22 arranged in an inlcined or angularspaced relation with the leads 23, 24, and 25 coupling the coils inseries, it being understood that one of the leads 24 or 25 will becoupled through a current control device in the same manner as for thecoils in FIG. 1. If the coils 21 and 22 are inclined in a relative angleof 15, the flux density will be linear but with slope profiles inaccordance with the current applied, as shown in FIG. 4, If the coils 21and 22 are adjusted to a 30 relative angle, the flux density willprovide a linear profile of sloped curves in accordance with the currentapplied, as shown in FIG. 5,

although the coils may be adjusted to any angle of inclination to meetdesired slopes or tapers of the flux field. It is to be noted that insuch parallel or angular relation of the coils the fields produced arelinear with current and will display a constant slope or taper for agiven inclination of the coils and further will only have a positiveslope across the discharge bore.

Referring in particular to FIG. 6 there is illustrated a foldeddischarge scanning laser tube 31 having reflecting surfaces 32, 33, 34,and 40 the surface 33 and 40 being partially reflective to permit theinput lasing beam 35 to pass through and be reflected on the surfaces32, 33, and 34 and discharge as output 36. Solenoid coils 37 and 38 arecoupled in series to the common lead 3?, the upper coil 37 beingangularly disposed with respect to the coil 38 such that the foldedportion of the lasing tube 31 allows the optical path to pass throughthe center of the solenoid. The flux density profile would be producedas shown in FIGS. 4 and but lengthwise of the lasing tube 31 forcross-field control of the lasing plasma by longitudinal increase influx density. Since it is desirable to drive the scanning plasma with aramp or sawtooth waveform, the displacement of the discharge 36 shouldbe linear with current so that it is known at all times where thedischarge is and by doubling the current it can be expected that theangular deflection of the discharge will be twice as great. The foldeddischarge laser tube 31 of FIG. 6 is of the scan laser type for which itis desirable to have the time varying field frequency to be as large aspossible so that a kilocycle or greater scan rate can be achieved whichis possible by air core type coils, such as the solenoids shown herein.The limiting factor for obtaining rapidly varying magnetic fields isinvariably the high inductance of the device which would be encounterdwith iron core electromagnets. The inductance of an air core solenoid isgiven by the equation:

L=u n lA where L is the inductance in henrys, p. is the permeability, nis the coil turns, 1 is the mean length in centimeters, and A is thecross sectional arrangement of the magnetic path. The frequency responseof Iron core electromagnets is limited and linearity of the flux densityis not possible with reasonable structures. The inductance of air corecoils depends on geometrical factors only, being independent of appliedcurrent. Hence, we may drive such solenoid coils at high rates usingfast high current low voltage power supplies.

Referring to FIG. 7 there is illustrated a plot of the new varyingmagnetic field geometry for a horizontal line scanner using thespecially inclined air core solenoid, as shown in FIG. 6. Plotted in theZ direction is the magnitude of the vertical component of the appliedmagnetic fields as a function of channel length Y and the channel widthX. The projected curves show the adjustable constant magnetic fieldcontours with the new net field immediately thereunder. The plasmaposition at time t and the plasma position at time t, are projectedoutwardly to show the scan angle of a scanning laser. Four positionsalong the channel length Y from the zero position through the one-thirdL position, two-thirds L position and L position illustrate the timevarying field contours at some time t,. At some distance X along X, thepermanent field tapers off from the B maximum condition to the value l3which is stable for both the X and X, positions. The magnetic fieldstrength or flux density 8 illustrates the plasma position at thecathode which varies as illustrated herein. This type of magneticgeometry would produce a highly linear discharge scan.

Referring more particularly to FIG. 8 the lasing discharge tube 10 isillustrated as being positioned between the two solenoid coils 41 and 42with a permanent magnet 43 having ends terminating in the air coreopenings of the solenoids. By this arrangement ferrite permanent magnetsprovide the necessary constant stabilizing field. The solenoids 41 and42 are in series with the current control circuit in the same manner asshown in FIG. I to providea means for adjusting the field flux densityat the discharge by small amounts to make up for varying mixer,discharge current, flow velocity, etc. Such a peaking adjustment may beprovided by placing the ferrite permanent magnet within the hollow coilsof the solenoid coils 41 and 42 as shown and by adjusting the current inpositive and negative voltage directions to produce an adjustment ragneas shown in FIG. 9. When desirable, these solenoid coils 41 and 42 maybe angularly positioned to provide field slope or taper.

Referring more particularly to FIG. 10 the lasing discharge tube 10 isillustrated as lying between stacked solenoids 51 and 52 in parallelarrangement with stacked solenoids 53 and 54 although such stacks may beinclined with respect to each other in the same manner as shown by thesolenoids in FIG. 2 to accomplish the linearly sloped or taperedprofiles as shown in FIGS. 3, 4, and 5 to obtain additional fieldstrength with low current values. The flux denisty or gaussmeasurements, B, can be adjusted by the current control device.

The use of air core coils in parallel or inclined relation across thedischarge plasma path of lasing tubes provide a number of advantagesover the prior known electromagnetic lasing devices in that the air coredevices are of lighter weight, more compact in size, and are readilyadjustable for field magnitudes and taper with a very modest powerinput. The use of inclined or parallel air core solenoids for thegeneration of magnetic fields are quite suitable for use in cross-fieldscan lasers and cross-field lasers. The conception hereinabove disclosedfor this invention provides a time varying field that is linear withdistance. The air core solenoid coils may be wound to fit the. odd shapeof the angular discharge scan laser. The time varying field will notinterfere with the laser optics and the time varying field is linearwith current. The air core solenoid devices are of low inductancecapable of a high rate operation. A wide gently tapering field over alarge area crossing the lasing discharge tube may be easily achievedwith air core coils. The advantages more pertinent to cross-field lasersalone are that there is no saturation and the field is linear withcurrent. There is a uniform field across the gap face desirable forfields across lasing tubes. The use of air core solenoids in adjustableangular relation provide readily adjustable taper or slope of themagnetic field. The magnetic field is independent of core diameter,area, or shape. As hereinabove disclosed, the coils may be readilystacked to increase the field capability and permanent ferrite magnetsmay be placed within the coil where peaking adjustment" are desirable.The use of air core coils make iron return flux paths unnecessaryreducing the weight and cost in such lasing devices.

The operation of the lasing devices herein illustrated is believedobvious from the above detailed description and requires no furtherdescription of operation herein. It is believed to be understood thatany of the fields desired across the lasing discharge tube may bereadily accomplished with good linear flux density results at inclinedflux profiles lengthwise of the lasing tube or crosswise of the lasingtube in any degree of angulam relation as illustrated in FIGS. 3, 4, and5. Accordingly, lasers discharge stabilization and beam scanning can bereadily accomplished by the concept hereinabove disclosed to providegreatly improved lasing action.

While many modifications may be made in the constructional details inthe placement and angular relation of air core coils to provideparticular profiles of slope or taper in magnetic fields across lasingdischarge tubes without departing from the invention, I desire to belimited in the spirit of my invnetion only by the scope of the appendedclaims.

I claim:

1. In a gas laser tube with an applied magnetic field, means forgenerating a varying magnetic flux field that is linear with distancecomprising:

at least one pair of solenoid coils with air core centers, said solenoidcoils being spaced across said laser tube to produce a transverse fluxfield across the gap between said coils and across said tube, means foradjusting said solenoid coils in angular re lation with respect to eachother to vary the slope profile of said field in a linear manner withtime and distance along and across said laser tube; and means forselectively varying the current flow through said solenoid coils forproducing constant linear magnetic flux field contours of chosen slopesand at adjusted field strength across said laser tube. 2. A means forgenerating a varying magnetic flux field as set forth in claim 1 havingmeans for adjusting said at least one pair of solenoid coils in angularrelation for producing the flux density of said field in a linearprofile along the longitudinal direction of said laser tube.

3. Ameans for generating a varying magnetic field as set forth in claim1 wherein said at least one pair of solenoid coils have a perma nestedpairs of solenoid coils.

1. In a gas laser tube with an applied magnetic field, means forgenerating a varying magnetic flux field that is linear with distancecomprising: at least one pair of solenoid coils with air core centers,said solenoid coils being spaced across said laser tube to produce atransverse flux field across the gap between said coils and across saidtube, means for adjusting said solenoid coils in angular relation withrespect to each other to vary the slope profile of said field in alinear manner with time and distance along and across said laser tube;and means for selectively varying the current flow through said solenoidcoils for producing constant linear magnetic flux field contours ofchosen slopes and at adjusted field strength across said laser tube. 2.A means for generating a varying magnetic flux field as set forth inclaim 1 having means for adjusting said at least one pair of solenoidcoils in angular relation for producing the flux density of said fieldin a linear profile along the longitudinal direction of said laser tube.3. A means for generating a varying magnetic field as set forth in claim1 wherein said at least one pair of solenoid coils have a permanentferrite magnet with the pole pieces terminating in the air core openingsthereof whereby a stabilizing field for a peaking adjustment of saidconstant magnet flux field contour of chosen slope is provided.
 4. Ameans for generating a varying magnetic flux field as set forth in claim1 wherein said at least one pair of solenoid coils are stacked andnested pairs of solenoid coils.